U.S. patent number 4,971,820 [Application Number 07/360,539] was granted by the patent office on 1990-11-20 for animal feeds and processes for their manufacture.
This patent grant is currently assigned to Canada Packers Inc.. Invention is credited to Kenneth S. Darley, Harvey G. Dorrell, Varoujan Jebelian, Henry J. A. Likuski.
United States Patent |
4,971,820 |
Likuski , et al. |
November 20, 1990 |
Animal feeds and processes for their manufacture
Abstract
Animal feed pallets such as fish feeds, dog and cat foods in
pellet form and textured soya protein pellets, are prepared by a
process in which edible liquid is added to the pellets and absorbed
under conditions of reduced pressure. In this way, larger amounts
of edible liquids such as lipids can be incorporated into the
pellets without significant deterioration in other desirable
properties of the pellets such as hardness and durability.
Inventors: |
Likuski; Henry J. A. (Weston,
CA), Jebelian; Varoujan (Willowdale, CA),
Dorrell; Harvey G. (Mississauga, CA), Darley; Kenneth
S. (Ajax, CA) |
Assignee: |
Canada Packers Inc.
(CA)
|
Family
ID: |
23418412 |
Appl.
No.: |
07/360,539 |
Filed: |
June 2, 1989 |
Current U.S.
Class: |
426/281; 426/302;
426/516; 426/523; 426/646; 426/454; 426/518; 426/601; 426/805 |
Current CPC
Class: |
A23K
40/30 (20160501); A23K 20/158 (20160501); A23K
40/20 (20160501); A23K 50/80 (20160501); A23K
40/25 (20160501); A23K 50/42 (20160501); Y10S
426/805 (20130101); Y02A 40/818 (20180101) |
Current International
Class: |
A23K
1/18 (20060101); A23K 1/00 (20060101); A23K
1/16 (20060101); A23K 001/00 () |
Field of
Search: |
;426/516,518,281,302,601,454,646,805,305,307,523 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
3306027 |
|
Aug 1984 |
|
DE |
|
0041467 |
|
Mar 1985 |
|
JP |
|
835405 |
|
Jun 1981 |
|
SU |
|
Primary Examiner: Penland; R. B.
Attorney, Agent or Firm: Bacon & Thomas
Claims
We claim:
1. A process for preparing animal feed pellets of improved physical
or nutritional characteristics, which comprises surface treating
solid edible feed pellets with a controlled quantity of an edible
liquid and subjecting the treated pellets to conditions of
subatmospheric pressure to absorb edible liquid into the pellets,
and recovering the pellets containing absorbed liquid in solid,
discrete form.
2. The process of claim 1 wherein the pellets initially are
produced by a process of extrusion followed by chopping into
pellets after emergence from an extruder die, and subsequently
treated under subatmospheric pressure conditions with edible liquid
for absorption thereinto.
3. The process of claim 2 wherein the pellets comprise fish feed
containing nutritive fish oil, and the edible liquid with which the
pellets are treated at sub-atmospheric pressure is also nutritive
fish oil.
4. The process of claim 2 wherein the pellets comprise animal pet
food which has been cooked in the extruder.
5. The process of claim 1 wherein the pellets are of textured
vegetable protein, and the edible liquid is water.
6. A process for preparing animal feed pellets having a solid
edible proteineous base and a high edible lipid content, which
comprises surface treating preformed solid animal feed pellets
containing from about 10-18% by weight of liquid lipid with a
controlled quantity of an edible liquid lipid and subjecting the so
treated pellets to conditions of subatmospheric pressure to absorb
the liquid lipid into the pellets, and recovering the pellets in
solid, discrete form and having a total content of liquid lipid of
from about 20-50% by weight.
7. The process of claim 6 wherein the pellets are initially
produced by a compactionpelletization step and fed from the
pelletizing step to the subatmospheric pressure, liquid absorption
step.
8. The process of claim 6 wherein the pellets comprise fishfeed
containing nutritive fish oil, and the edible liquid with which the
pellets are treated at subatmospheric pressure is also nutritive
fish oil.
9. Discrete, free flowing pellets for feeding to animals,
comprising feed pellets containing edible lipids, said edible
lipids present in the pellets in an amount of from about 20-50% of
the total weight thereof, said pellets retaining a hardness and
surface structure which allows their packaging in bulk without
substantial coalescence or collapse.
10. Pellets according to claim 7 having a Stokes hardness of from
4.5 to 7.1.
11. Pellets according to claim 10 prepared by a
compaction-pelletization process and having lipid content of from
20-35 per cent of the total weight of the products.
12. Pellets according to claim 10 prepared by an extrusion process
and having a total lipid content of from 30-50 per cent of the
total weight of the products.
Description
FIELD OF THE INVENTION
This invention relates to solid, particulate food products suitable
for feeding to animals such as fish, poultry, dogs, cats, swine,
etc., and to processes for the production thereof. More
particularly, it relates to a process of producing feed pellets of
improved physical characteristics and nutritional value.
BACKGROUND OF THE INVENTION
Feed materials that are commercially manufactured for domestic
animals such as fish, dogs, cats, poultry and swine frequently
contain the maximum amount of lipid that can be incorporated into
the materials without altering their desired physical form. This is
done for purposes such as lowering the cost of the materials,
maximizing animal performance results, and minimizing the amount of
excrement voided by the animals.
In the case of fish farming, compacted feed materials commonly
consist of feed pellets of standard size and uniform composition,
for ease of administration to and diet control of the fish. The
lipid ingredients are typically of marine origin, such as fish
oils. Standard fish feed pellets commonly contain 10-18% by weight
of fish oil. Increases in this level, desirable to increase the
nutritional value of the feed per unit weight, adversely affect the
structural integrity of the pellets, in terms of hardness and
surface oiliness. Then the pellets tend to lose their free-flowing
nature during transportation.
The commonly adopted process for making fish feed pellets is one of
mixing the ingredients and then pelletizing them. Pelletizing is
essentially a process of compaction. The pellets are compressed to
certain hardness, porosity and density over which there is little
control or flexibility. Most of the oil content must be included in
the mixture prior to pelletizing, but attempts to include larger
amounts than about 10-18% lead to the formation of pellets of
insufficient hardness and durability. Whilst small amounts of
additional oil can be incorporated by adding oil subsequently to
the pellets, this is a time-consuming step. The subsequently added
oil only attaches to and becomes absorbed in the pellets slowly,
and for the most part remains on the surface, as it cures, over
about 48 hours. Before that process is completed, the pellets
cannot acceptably be bagged and shipped.
Some pelletized fish feeds and other pelletized pet foods are
conventionally made by an extrusion method. In the extruder, the
ingredients may be mixed, cooked, sheared, gelatinized, and formed
and chopped into pellets, rather than simply compacted and chopped
into pellets in a pelletizing process. The extrusion process allows
more control over density and porosity of the product, than in the
case of pelletizing, although it is a more expensive process and
requires more expensive equipment. For example, the control can be
exercised by varying the degree of cooking, or by varying the
extruder outlet conditions to provide for greater expansion of the
product on issue from the extruder, so as to form a less dense
product. Additional oil can be added to an extruded pelletized
product, but again the amount is limited by surface effects.
Other pet food products which are handled in pellet form include
textured vegetable proteins such as textured soya protein (TSP),
which is basically a fully cooked defatted soya protein. This is
used as a meat extender in canned dog foods and cat foods. TSP is
prepared by cooking and extruding the material, then dehydrating it
in pellet-like form for storage and transportation. It is
re-hydrated prior to addition to the food cans. If its density
after re-hydration is not correct, it will not mix adequately with
the other ingredients.
Further, various pet foods for dogs and cats are produced in hard
pellet forms, and contain varying quantities of lipids. Poultry
feeds and swine feeds similarly are prepared and used in pellet
form. In all these cases, it is often desirable that the pellets be
of uniform, controlled composition, with high lipid content.
It is an object of the present invention to provide a novel process
for preparing animal feed pellets.
It is a further object of the invention to provide such a process
which can yield feed pellets of improved nutritional content and
controlled density and texture.
SUMMARY OF THE INVENTION
The present invention provides a process whereby edible liquids are
added to feed pellets and absorbed into the pellets under
conditions of reduced atmospheric pressure. The feed pellets are
first formed by a conventional compacting-pelletizing process, or
by an extrusion process, and then treated with edible liquid under
reduced pressure. The process has been found to give unexpected
advantages in the pelletized products, both in connection with the
nature and composition of the product, and in the ease and economy
with which the process can be conducted and the flexibility of
conditions which can be adopted to give a wide variety of feed
products.
In connection with oil-containing fish feed pellets, for example,
the process of the present invention permits larger amounts of
lipid to be added, without destroying the integrity of the pellets,
and by use of the simple compaction-pelletizing process. In
connection with extruded pellets of animal feed, the process allows
for control of the density of the pellets, independently of the
composition and texture thereof, whilst allowing absorption of
relatively large volumes of edible lipids into the pellets. With
TSP, the adjustment of the water content of the pellets by the
process of the invention again allows independent control over the
density of the end product, for improved mixing with the other
canned pet food ingredients.
Thus according to one of the aspects of the present invention,
there is provided a process for preparing feed pellets of improved
physical or nutritional characteristics, which comprises treating
solid edible feed pellets with a controlled quantity of an edible
liquid and subjecting the treated pellets to conditions of
sub-atmospheric pressure to absorb edible liquid into the pellets,
and recovering the pellets containing absorbed liquid in solid,
discrete form.
According to another aspect, the present invention provides
discrete, free flowing feed pellets for feeding to animals, the
feed pellets containing edible lipids in an amount of from about
20-50 cent of the total weight thereof, and having a and surface
structure which allows their packaging bulk without substantial
coalescence or collapse.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
One preferred application of the process of the present invention
is in the manufacture of fish feed pellets, e.g. salmon feed, for
fish farming operations. Some of the lipid in the form of fish oil,
typically 8-15% by weight of the total product, is incorporated in
the mix prior to pelletizing. The conventional
compacting-pelletizing process produces dense pellets, which will
not absorb lipid subsequently applied into the interior of the
pellets, to any significant extent. The only additional lipid which
can be applied is surface lipid, which must be left to cure on the
pellet surface. This curing process takes about 48 hours. By use of
the process of the present invention, additional lipid can be
incorporated, which will penetrate into the body of the pellets and
not remain substantially at the surface, so that the content of
total lipid can be substantially increased. When the pellets have
been produced by a compacting-pelletizing process, their total
lipid content can be increased to 20-35% of the total weight of the
products, by use of the process of the invention. When the pellets
have been produced by an extrusion process, their total lipid
content can be increased even more by the process of the invention,
e.g. up to 50% of the total weight or even higher.
The physical structure and integrity of the pellets is not harmed.
The resulting, high-oil content pellets are of satisfactory
hardness and surface structure to allow their packaging and
transportation in bulk, a short time after preparation. The process
of subjecting the pellets to vacuum conditions on or after
application of the additional oil minimizes the formation of oily
surfaces and loss of hardness, at least to a sufficient extent to
maintain the integrity of the pellets satisfactorily for practical
purposes.
If desired, the fish feed pellets may be mixed with a conventional
drying agent, such as fine particle size silica, before or after
the vacuum drying, and before or after the pelletizing process.
In the preferred procedure according to this aspect of the
invention, both the pellets and the supplementary fish oil are
heated prior to being mixed together. This accelerates the uptake
of oil by the pellets, without noticeably affecting the pellet
structure. The pellets should be heated preferably to at least
15.degree. C. and most preferably to close to but not exceeding
70.degree. C. prior to addition of supplementary fish oil to the
pellets. The supplementary fish oil is suitably at a similar
temperature at the time of mixing, but not, of course, at
temperatures above its boiling point or decomposition temperature.
Then the pellets are subjected, after soaking in supplementary fish
oil, to reduced pressure conditions, i.e. vacuum pressure. This
vacuum process suitably takes place at temperatures of from about
15-70.degree. C. in a vacuum oven, under a vacuum pressure of from
about 0-20 kPa, for about 1-30 minutes. Commercial apparatus is
readily available which is suitable for this step, and in which the
vacuum pressure is adjustable. A specific example is the apparatus
sold under the trade mark VARIO-VAC, manufactured by Dorit
Maschinen Handels ag.
Instead of the 48 hours' treatment time required for contact of the
supplementary fish oil with the pellets according to conventional
processes, whilst the oil cures and hardens, the process of the
present invention permits the supplementary oil to be incorporated
into the pellets in a time period of less than ten minutes,
typically 2-4 minutes. In practice, the feed pellets are arranged
to issue from the pelletizing machine at an appropriate
temperature, usually allowed to harden for a few minutes and then
fed directly into the vacuum oven preadjusted to the correct
temperature. The pre-heated edible oil is added to the pellets in
the vacuum oven, and then the vacuum oven is closed and the
appropriate vacuum is drawn. After opening and emptying the oven of
the pellets, they are ready for bagging and transportation. No
substantial modification is necessary to the remainder of the
pelletizing apparatus and packaging, and the process is conducted
extremely rapidly and efficiently according to the invention.
The process of the present invention also adds considerable
flexibility to the pelletizing process and the formulations which
can be made. In animal feed other than fish feed, e.g. cat food,
dog food, swine feed, poultry feed etc., lard is the commonly
chosen lipid for inclusion in the pellets. For use in the present
invention, the lard added for incorporation into the pellets after
the pellets have been formed is appropriately in the liquid phase.
By use of the present invention, less lipid needs to be
incorporated in the feed mixture prior to pelletizing, since more
lipid can be added after pelletizing. Accordingly, a formulation
can be chosen prior to pelletizing which leads to improved
durability and firmness of the final pellets. The amount of fines
generated on pelletizing can be minimized, by adding less lipids to
the base mixture prior to pelletizing. Pellets of better texture
are thereby produced, and their high lipid loading can be restored
or improved compared with conventional pellets, by the subsequent
lipid treatment and absorption under reduced pressure according to
the invention. The smaller the quantity of the lipid in the mix to
be pelletized, the harder and more durable the pellets which can be
made. The post-addition of the lipid according to the present
invention does not significantly impair the durability of the
pellets. Accordingly, the amount of lipid added before pelletizing
as compared with the amount of lipid added after pelletizing and
with absorption under reduced pressure according to the invention
can be adjusted relative to each other, to obtain the desired
combination of durability, texture and lipid quantity in the final
pellets.
When the process of the present invention is applied to extruded
pelletized products, similar advantages are obtained. In
particular, since the lipid can be added in whole or in part to the
extruded pellets after their formation and extrusion, a greater
degree of flexibility on the conditions and ingredients in the
extruder can be exerted, to prepare improved products. In
particular, it allows control over the porosity and density of the
pellets which can be produced. In the prior art processes, where it
was desirable to include a substantial part of the lipid in the
mixture prior to extruding and pelletizing, the range of porosity
and density of products which could be produced was limited by the
presence of this lipid. With the process of the present invention,
where substantial quantities of the lipid are added after
extrusion, more changes and variations in the conditions in the
extruder can be effected without concern for the effects they may
have on the lipid within the product at that time. It is generally
preferred to precondition the mixture by steam treatment prior to
extruding. This has a beneficial effect on the durability of the
final pellets. Exposure to steam for a period of 30 seconds-1
minute is typically suitable. This raises the temperature of the
mix prior to extruding, so as to provide further flexibility in
extruder operation. Water treatment can be used instead of steam
treatment, to produce denser pellets.
For example, the density of the extruded pellets can be adjusted by
arranging for the material to expand as it issues from the
extrusion die. In this way, a light product can be made,
sufficiently light to float on water, which is a desirable
characteristic of some fish feeds. The degree of expansion on
issuing from the extruder die, and hence the density of the
product, can be adjusted by adjusting the amount of cooking which
takes place in the extruder, or by adjusting the quantity of
expansible materials in the mix, for example starch. In other
circumstances, fish feed pellets which will sink slowly or rapidly
through a body of water may be desirable. The conditions and
ingredients in the extruder can again be adjusted to prepare such
feed pellets. Since, in the process of the invention, a certain
fixed amount of lipid does not have to be added to the extruder, an
extra degree of freedom is available to vary and adjust other
characteristics of the final feed pellets. Moreover, as shown in
the following specific examples, the addition of oil to the pellets
and vacuum absorption thereof, according to the present invention,
itself increases the sink rate of the pellets in water,
independently of the formulation or conditions in the extruder.
Moreover, the production of a pelleted product by use of an
extruder enables large amounts of lipid to be added subsequently,
by the process of the invention, i.e. by absorption under reduced
pressure. In addition, the density of the pellets themselves can be
adjusted, by the amount of vacuum pressure which is drawn on the
pellets after extrusion and by the amount of oil which is absorbed
under reduced pressure by the pellets. This ability to adjust
density and lipid content after extrusion allows for greater
flexibility in the operating conditions of the extruder, use of
cheaper ingredients and selection of most efficient or most
economical extruding conditions, without paying serious regard to
the consequential effects on pellet density.
The process of the invention appears to have the effect of
withdrawing air from the pores of the pellets, thereby allowing
greater penetration of lipids such as oils into the pores of the
pellets. Accordingly, a more even uptake of lipid is achieved,
without affecting the surface of the pellets. It allows greater
quantities of lipid to be admitted to the pellets, even in
comparison with the amounts which can be added by combination of
pre-addition and post-addition to the pellets by prior art
processes. The removal of substantial quantities of air from the
pores of the pellets increases the shelf life of the final product
and decreases the tendency towards rancidity.
Another area of preferred application of the present invention is
in the preparation of textured vegetable protein. This material is
usually defatted soya meal, and in its preparation for
incorporation into pet foods it is fully cooked and extruded into
pellet-like form, and then dehydrated. At extrusion, it typically
has a water content of 30% by weight, and it is dehydrated
typically to an 8% water content. Then it is in a form convenient
for shipping from the textured vegetable protein-producing facility
to the pet food preparation and canning facility.
Prior to or during its addition to pet food meat preparations, it
is hydrated. The dehydrated material is a very porous material, and
will re-absorb 2-3 times its own weight of water. As it does so,
its density changes. Accordingly, if the material is insufficiently
re-hydrated prior to addition to the pet food mixture, it will
float on the material and be insufficiently homogeneously mixed
into the food mix. If too much water is added to hydrate the
textured vegetable protein, its density may be so high that it may
interfere with the can filling operation.
The present invention provides a process whereby dehydrated
textured vegetable protein may be evenly and carefully rehydrated,
by addition of water thereto and drawing of a vacuum on the
mixture. In this way, the density of the re-hydrated textured
vegetable protein can be carefully controlled to the right level
prior to its addition to the remainder of the food mixture. In this
way it can be properly and evenly mixed in the food product, and
will not interfere with the filling process.
The invention is further described for illustrative purposes only
in the following specific examples.
EXAMPLE 1
Salmon feed pellets with fat contents of 14% and 17% were obtained
by pelleting (laboratory pellet mill with a 4 millimeter die) feed
mixtures consisting mainly of herring meal and herring oil and
further containing about 10% moisture, about 12% inorganics, about
14% carbohydrates, balance protein. The pellets were stored at a
room temperature of 21.degree. C. and tested for hardness, as
measured in kilograms with a Stokes hardness tester on four
consecutive days and on the tenth day after pelleting. As a major
part of this study, a portion of both the 14% fat and the 17% fat
pellets were coated with herring oil (for 20 minutes in the vacuum
oven at 54.degree. C. with the Marsh vacuum gauge at 30 inches,
equivalent to about 0 kPa) to obtain pellets with a final fat
content of approximately 25% in each case. This was done with
separate batches of pellets on the first, second, third, fourth and
tenth day after pelleting. The fat-coated pellets were tested for
hardness as given above.
In the case of the pellets that were not coated with herring oil,
pellet hardness increased from the first day until the third day
after pelleting and then remained constant. With the 14% fat
pellets, the hardness increased from Stokes readings of
approximately 5.5 to 6.5 With the 17% fat pellets, the hardness
increased from 5.0 to only 5.5.
In the case of the 25% fat pellets coated with herring oil and
vacuum dried, pellet hardness similarly increased from the first
day until the fourth day after pelleting, and then remained
constant. With the 14%-fat pellets to which approximately 11%
herring oil was applied to the surface, the hardness increased from
5.0 to 6.0. With the 17%--fat pellets coated with approximately 8%
herring oil, the hardness increased from approximately 4.5 to
5.5.
This shows that pellet hardness is increased by manufacturing the
pellets from a feed mixture with a low amount of oil. This hardness
is substantially retained after further oil is applied to the
pellets' surface via the use of vacuum pressure.
EXAMPLE 2
Salmon-feed pellets, of approximately the same composition as
reported in Example 1, were heated to temperatures of approximately
21.degree. C. and 60.degree. C. and placed in open-top plastic
containers. Herring oil at 21.degree. C. and 60.degree. C. was
mixed into the pellets at a level of 10%. This initially increased
the lipid content of the 32 samples of pellets from 18% to 28%).
The oil-coated pellets were placed in a vacuum-oven for time
intervals of 10 minutes and 20 minutes (times which on subsequent
experience are unnecessarily long). The vacuum-oven temperature was
60.degree. C; the vacuum-gauge setting was 30 inches, equivalent to
about 0 kPa. After vacuum-drying for either 10 minutes or 20
minutes, all of the samples of oil-coated pellets appeared to be
dry and ready for bagging. Thus, they were immediately placed in
small plastic bags, the bags were heat-sealed, and the samples were
stored for 18 hours at 21.degree. C. The bags were then opened, the
oil-coated pellets were examined, and the amount of herring oil
retained on the pellets was estimated from their gain in
weight.
Pellet quality was very good. The amount of herring oil retained by
the pellets was 6.6%, regardless of the experimental procedure that
was used, thus increasing the total lipid content of the pellets to
24.8%, a value not achievable in good quality pellets without the
use of vacuum pressure.
EXAMPLE 3
A standard 17.5%-fat (by acid hydrolysis) salmon feed of
composition essentially as described in Example 1 was mixed and
pelleted on pilot-plant scale (commercial pellet mill with a 7
millimeter die). One hour and 4 days after pelleting, the
salmon-feed pellets were coated with 7.0% herring oil. This was
accomplished by placing the pellets at 18.degree. C. and the
herring oil at 82.degree. C. in a Vario-Vac,. The ingredients were
mixed together for approximately 5 minutes while the vacuum was
gradually increased over a period of 4 minutes to 9 kPa. Mixing was
continued for a further 5 minutes under this vacuum. The mixing and
vacuum pressure were then discontinued, and a sample of the
fat-coated pellets was obtained to determine the "oiliness" and
hardness of the pellets. Fine particle size silica at a level of
0.8% was mixed into the remaining pellets for 2 minutes, and a
further sample of fat-plus-silica coated pellets was obtained to
determine the "oiliness" and hardness of the pellets.
As indicated above, the pellets were coated with herring oil
without and with silica one hour and 4 days after they were
manufactured. Visual inspection was used to assess the "oiliness"
of the pellets immediately after they were coated with these
materials. The Stokes hardness tester was used to determine the
hardness of the pellets within 2 hours after they were coated with
herring oil, and for 5 consecutive days thereafter in the case of
the pellets coated with herring oil one hour after they were
manufactured. Only two such measurements were taken for pellets
coated with herring oil 4 days after manufacture. The hardness of
pellets without surface fat was determined.
After vacuum-drying, the surface of the herring oil-coated pellets
was judged to be a bit oily but not too "oily" for the pellets to
be bagged. The addition of fine particle size silica to the pellets
immediately removed all traces of "oiliness" from the pellets. The
base pellets without surface fat had an average Stokes hardness
reading of 6.0 on the day of pelleting. This value gradually
increased to 7.1 on days 4 and 5 after pelleting. The pellets
coated with herring oil one hour after pelleting had an average
Stokes hardness reading of 5.6 on the day of pelleting. This value
also gradually increased to 6.2 on days 4 and 5 after pelleting.
The pellets coated with herring oil 4 days after pelleting had an
average Stokes hardness reading of 6.5 on days 4 and 5 after
pelleting. The addition of fine particle size silica did not
noticeably affect the hardness of the pellets.
EXAMPLE 4
Fish feed pellets, in 7 millimeter sizes and 11 millimeter sizes,
were manufactured with a single screw extruder and tested for
various physical characteristics of importance in commercial fish
feeds, e.g. buoyancy.
The 7-millimeter pellets were manufactured from a fish feed base
mixture that mainly contained herring and capelin fish meals. The
feed mixture contained 15% fat. It was ground in a Fitz mill to a
maximum particle size of 1.5 millimeters prior to being
extruded.
The 11-millimeter pellets were manufactured from a fish feed base
mixture that mainly contained menhaden fish meal. The feed mixture
contained 12% fat. It was ground in a hammer mill to a maximum
particle size of 1.5 millimeters prior to being extruded.
For the manufacture of the 11-millimeter pellets, one feed mixture
was conditioned with steam prior to being extruded. Herring oil was
added to the feed mixture at a level of 3% during the conditioning
process. The second feed mixture was conditioned with water instead
of steam. This was done to increase the density of the pellets.
Two separate 100-gram samples of each of the three extruded fish
feeds so prepared were coated with herring oil at a level of 20%
(25 grams of herring oil per 100 grams of salmon feed). One of the
samples from each of the groups was placed in vacuum desiccator and
subjected to a vacuum pressure of 13 kPa for a time of 6
minutes.
The fat-coated pellets were visually assessed for surface
"oiliness". Then the rate at which they sank through 1.5 metres of
water with 4% salt was determined. For this purpose, 5 pellets were
chosen at random from each of the treatments. The rate of sink
values were compared with those determined for ten of the same
extruded pellets without surface fat.
The results are presented in Table 1.
TABLE 1 ______________________________________ The "Rate of Sink"
of Extruded Pellets without and with Surface Fat Pellet Size and
Conditioning Method 7-mm 11-mm Steam Steam Water
______________________________________ Base Pellets Without Surface
Fat Fat Content (%) 15 15 12 % that Sank in Salt Water 60 0 40 Time
to Sink 1.5 m (Sec) 29 .+-. 7* -- 25 .+-. 9 Pellets Coated with Fat
Estimated Fat Content (%) 35 35 32 % that Sank in Salt Water 100
100 100 Time to Sink 1.5 m (Sec) 26 .+-. 10 27 .+-. 11 17 .+-. 6
Surface Appearance Oily Oily- Dry some free oil Pellets Coated with
Fat Under a Vacuum Estimated Fat Content (%) 35 35 32 % that Sank
in Salt Water 100 100 100 Time to Sink 1.5 m (Sec) 17 .+-. 1 11
.+-. 1 16 .+-. 7 Surface Appearance Dry Oily Dry
______________________________________ *Means with Standard
Deviations
None of the fat-coated pellets floated on the surface of the water
as occurred with the extruded pellets without surface fat. Extruded
7 mm and 11 mm pellets that were manufactured by conditioning the
feed mixture with steam sank through 1.5 m of 4% salt water in
approximately 26 seconds when their surface was coated with 20%
herring oil. They sank through 1.5 m of 4% salt water in
approximately 14 seconds when their surface was coated with herring
oil by the use of a vacuum. The latter value is a desirable
rate-of-sink for extruded salmon feeds.
These results indicate that the rate of sink of high fat content
(35%) salmon feed pellets can be increased by more than 50% by
applying the vacuum pressure technique to oil-treated pellets
according to the invention. The process can also provide high fat
content pellets of improved durability. Accordingly, the operator
has the freedom to adjust the extruder operating conditions and
formulation with a view to providing pellets of the required
hardness and durability, without at the same time being concerned
with consequential effects on the density and buoyancy of the
products. That adjustment, along with the raising of the fat
content to previously unattainable levels, can if desired be
achieved by the post-treatment oil absorption under vacuum. This
provides the operator with additional opportunities to custom
manufacture products to a customer's specification.
EXAMPLE 5
The effect of varying the amount of vacuum pressure and vacuum time
on the amount of herring oil retained on the surface of 15% fat
extruded fish feeds that are further coated with approximately 15%
herring oil, and on other physical characteristics of the pellets
was studied.
Extruded 15% fat fish feed pellets, 11 mm in size, were coated with
15% herring oil by mixing the pellets and herring oil together
without and with vacuum pressures of 70 kPa, 35 kPa and 7 kPa for
times of 2 minutes and 4 minutes. The effect of the above processes
on the amount of fat retained in the pellets, and various physical
characteristics of the pellets, was then determined.
These extruded pellets were the same as those used in Example 4.
They were manufactured from essentially the same feed mixtures that
were used to manufacture the previously reported samples. Eight 25
g samples of the extruded pellets were separately placed in a glass
flask of a laboratory-sized rotary evaporator. The temperature of
the pellets and flask were near 22.degree. C.
Herring oil at 22.degree. C. was separately added to each sample of
pellets at a level of 15%. The pellets and herring oil were mixed
together without and with vacuums of 70 kPa, 35 kPa and 7 kPa for
times of 2 minutes and 4 minutes. The mixing was done without
agitating the pellets, by slowly rotating the glass flask on the
rotary evaporator. The pellets and herring oil were mixed together
for times of 2 minutes and 4 minutes, after the desired vacuum
pressures were attained.
When the mixing was complete, the vacuum was released and the fat
coated pellets were placed on Whatman No. 54 filter paper. They
were gently rotated on the filter paper, at 15-minute intervals,
for approximately 1 hour. The amount of fat retained on the
fat-coated pellets was then determined by both weighing the pellets
and weighing the amount of fat absorbed on the filter paper.
The fat-coated pellets were visually assessed for surface oiliness.
Then the rate at which they sank through 1.5 m and 1.0 m of water
with 4% salt was determined. Five pellets were selected at random
for each of the 1.5 m and 1.0 m determinations. The latter
determination was made after the pellets had sunk through 0.5 m of
water. The "dwell time" of the pellets was subsequently calculated
as the time, in seconds, it took the pellets to sink 1.5 m minus
1.5 times the time, in seconds, it took the pellets to sink the
latter 1.0 m. This value indicates whether or not the pellets tend
to be more buoyant when first placed in water than after they are
in the water for a short period of time.
In addition to "dwell time", in this example a "true hardness"
value was determined for the pellets. "True hardness" is a typical
pellet hardness reading obtained with a Stokes hardness tester
minus an initial reading obtained when the jaws of the Stokes
hardness tester first contact the pellet without noticeably
applying pressure to the pellet.
The results are presented in Table 2.
TABLE 2
__________________________________________________________________________
THE PHYSICAL PROPERTIES OF EXTRUDED 11-MM PELLETS WITH 15% FAT THAT
WERE STEAM CONDITIONED PRIOR TO MANUFACTURE AND THEN FURTHER COATED
WITH 15% HERRING OIL
__________________________________________________________________________
Procedure Used to Coat Surface Fat Vacuum (kPa) 100 100 70 70 35 35
7 7 Mixing Time 2 4 2 4 2 4 2 4 (minutes) Pellet Parameter
Determined Surface Oil 97 97 98 99 98 99 98 99 Retained (%)
Hardness* 5.9 .+-. 0.6 6.2 .+-. 0.2 5.8 .+-. 0.3 6.0 .+-. 0.6 6.0
.+-. 0.2 6.2 .+-. 0.3 5.8 .+-. 0.4 5.8 .+-. 0.4 "True Hardness" 2.9
3.2 2.8 3.0 3.0 3.3 2.8 2.8 Bulk Density -- -- -- -- -- -- -- 615
(G per Litre) % that Sank 80 20 80 100 100 100 100 100 in Salt
Water Time to Sink 29 .+-. 6 35 30 .+-. 2 19 .+-. 39 25 .+-. 8 21
.+-. 2 17 .+-. 4 18 .+-. 3 1.5 meters (sec.) Time to Sink 14 .+-. 3
16 12 .+-. 1 10 .+-. 1 16 .+-. 4 13 .+-. 2 11 .+-. 2 14 .+-. 3 1.0
Meter (sec.) "Dwell Time" 8 10 12 3 0 1 2 0 in Water (sec.) Surface
Slightly Oily Appearance
__________________________________________________________________________
*Hardness of base pellet was 6.0 .+-. 0.6
The results show that 30% oil content pellets can be prepared
without significantly decreasing the hardness of the pellets. Their
buoyancy can be adjusted by changing the vacuum coating
conditions.
EXAMPLE 6
The amount of fat retained on extruded dog and cat food pellets
that were coated with 15% and 30% melted lard was determined, by
mixing the pellets and lard together without and with vacuum
pressures of 70 kPa and 35 kPa for times of 2 minutes and 4
minutes.
The basic pellets used were a dog food with 15% fat, a puppy food
with 8% fat and a cat food with 6% fat. The dietary fat levels were
chemically determined by an acid-hydrolysis procedure. The pet
foods had calculated protein contents near 30%. Their main feed
ingredients were corn, wheat shorts, soybean meal, meat meal,
poultry meal and fish meal.
Twelve 25-gram samples of each pet food were separately placed in a
glass flask of a laboratory-size rotary evaporator. The temperature
of the pellets and flask were at room temperature.
Lard that had been melted at a temperature of 49.degree. C. was
separately added to each sample of pet food at levels of 15% (4.4
grams of lard per 25 grams of pet food) and 30% (10.7 grams per 25
grams). The lard, which was produced by extracting it from pig
skins, was "feed grade" in quality. It had a melting point of
28.degree. C, as determined on a Mettler PF 80 Drop-Point
apparatus.
The pellets and lard were mixed together without and with vacuums
of 70 kPa and 35 kPa for times of 2 minutes and 4 minutes. The
mixing was done without agitating the pellets, by slowly rotating
the glass flask on the rotary evaporator. The pellets and lard were
mixed together for times of 2 minutes and 4 minutes after the
desired vacuum pressures were attained.
When the mixing was complete, the vacuum was released and the
fat-coated pellets were placed on Whatman No. 54 filter paper. They
were gently rotated on the filter paper, at 15 minute intervals,
for approximately 1 hour. The amount of fat retained on the pellets
was then determined by both weighing the fatcoated pellets, and
weighing the amount of fat absorbed on the filter paper.
It was found that larger amounts of lard could be incorporated in
the pellets by surface application and vacuum pressure, with
retention of acceptable surface appearance, than in cases where
vacuum pressure was not used.
EXAMPLE 7
Extruded, defatted soybean meal pellets (TSP) were hydrated without
and with the simultaneous use of a vacuum, to determine the effect
on the amounts of water retained by and the specific densities of
the hydrated pellets.
Twenty 20-gram samples of TSP pellets were placed in glass
containers that were subsequently equally divided into four
separate groups. Ten grams, 20 grams, 30 grams, 40 grams or 60
grams of water were then added to the pellets in the containers in
each group. The pellets and water were mixed together for times of
4 minutes and 30 minutes without and with the use of 7 kPa of
vacuum. The vacuum was applied via the use of a rotary evaporator
for 4 minutes. In the case of pellets hydrated for 30 minutes, the
vacuum was applied during the final 4 minutes of the hydration
process.
Excess water was drained, via the use of sieve, from the hydrated
TSP pellets. The pellets were then weighed, and the percentages of
added water that they retained were calculated. After being
weighed, the pellets were stored in sealed plastic containers in a
refrigerator at 4.4.degree. C. for 16 hours. Then the pellets'
specific densities were determined. They were determined as the
weights of the pellets relative to the weights of the volumes of
water at room temperature (22.degree. C) that were displaced by the
pellets.
The results of this study are summarized in Table 3.
TABLE 3 ______________________________________ The Effects of
Hydration Time and Vacuum Pressure on the Amount of Water Retained
by and the Average Specific Density of TSP Pellets Time in Minutes
of % Water.sup.1 Specific Hydration Vacuum Retained Density.sup.2
______________________________________ 4 0 68.1 0.94 30 0 80.1 0.97
4 4 83.3 0.98 30 4 88.4 1.03 ______________________________________
.sup.1 Mean of the percentages of added water retained by TSP
pellets ove a pellet:water range of 1.0:0.5-1.0:3.0. .sup.2 Mean of
the specific densities of TSP pellets over a pellet:water range of
1.0:0.5-1.0:3.0.
It was determined that the percentage of added water retained in
TSP pellets decreases when greater amounts of water are added to
the pellets over a pellet:water range of 1.0:0.5-1.0:3.0. More
importantly, however, it was determined that both the percentages
of added water retained in TSP pellets and TSP pellet specific
densities are increased by the simultaneous use of vacuum pressure
during the hydration process. More water can be added in shorter
time, and the process can be tailored to obtain pellets of desired
hydration level and density, by varying the vacuum.
* * * * *